Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays, and the like).
Description of the Prior Art
Photoconductive materials, which constitute photoconductive layers in solid state image pickup devices, image forming members for electrophotography in the field of image formation, or manuscript reading devices and the like, are required to have a high sensitivity, a high SN ratio (photocurrent (I.sub.p)/dark current (I.sub.d)), spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. Particularly, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid safety characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a photoconductive material. For example, German OLS Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German OLS No. 2933411 discloses an application of a-Si for use in a photoelectric transducing reading device.
However, under the present situation, the photoconductive members of the prior art having photoconductive layers constituted of a-Si are further required to be improved in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with the lapse of time.
For instance, when the above photoconductive member is applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigue by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, a-Si has a relatively smaller coefficient of absorption of the light on the longer wavelength side in the visible light region as compared with that on the shorter wavelength side. Accordingly, in matching to the semiconductor laser commercially applied at the present time, the light on the longer wavelength side cannot effectively be utilized, when employing a halogen lamp or a fluorescent lamp as the light source. Thus, various points remain to be improved.
On the other hand, when the light irradiated is not sufficiently absorbed in the photoconductive layer, but the amount of the light reaching the substrate is increased, interference due to multiple reflection may occur in the photoconductive layer to become a cause for "unfocused" image, in the case when the substrate itself has a high reflectance for the light transmitted through the photoconductive layer.
This effect will be increased, if the irradiated spot is made smaller for the purpose of enhancing resolution, thus posing a great problem in the case of using a semiconductor laser as the light source.
Further, a-Si materials to be used for constituting the photoconductive layer may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical or photoconductive characteristics of the layer formed.
That is, for example, in many cases, the life of the photocarriers generated by light irradiation in the photoconductive layer formed is insufficient, or at the dark portion, the charges injected from the substrate side cannot sufficiently impeded.
In addition, when the layer thickness becomes about ten microns or more, float and peeling of the layer from the support surface or cracking of the layer are liable to be caused after the material is taken out of a vacuum deposition chamber for layer formation and when stored in air. These phenomena often occur particularly when the support is in a form of drum which is usually used in the field of electrophotography and the problem of the phenomena should be solved so as to improve its stability as to the lapse of time.
Therefore, it is necessary to improve the characteristics of the a-Si material itself while it is necessary to solve all the problems as mentioned above upon designing the photoconductive members.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state image pick-up devices, reading devices, etc.
It has now been found that a photoconductive member having a light receiving layer exhibiting photoconductivity which comprises an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atom, so-called hydrogenated amorphous silicon, halogenated amorphous silicon, or halogen-containing hydrogenated amorphous silicon (hereinafter comprehensively referred to as "a-Si(H,X)"), said photoconductive member being prepared by designing so as to have a specific structure as hereinafter described, not only exhibits practically extremely excellent characteristics, but also surpasses photoconductive members of the prior art in substantially all respects, especially having markedly excellent characteristics as a photoconductive member for electrophotography and also excellent absorption spectrum characteristics on the longer wavelength side.